Manufacture of sulfuric acid



1953 H. F. MERRIAM ETAL 2,629,651

MANUFACTURE OF SULFURIC ACID Filed July 15. 1949 souRcE F SULFUR 45MATERIAL H SUPPLY s0 GAS CONCENTRATING GENERATOR TowER BLOWER 52RADIATOR -I3 v COOLER 4e g F'T'"; 82 H 0 l 1 2 I L 74 5a 58 j "T"'! L':[7

l v g 22: I v r 70 L I L 1 f i 1 l "/5 l6-- COOLING COOLING l DRYINGTOWER TowER E TowER R i f i i I l l k l DISCARD E I +65 64 27 7e E 28 .E

SULFUR V I SUBLIMER 33 32 74 BLOWER SECONDARY COMBUSTION CHAMBER 40 No.1No.2 No.3 42 CONVERTER coNvERTER coNvERTER INVENTORS.

HENRY F. MERRIAM URBAN S. LAUBER ATTORN Y.

Patented Feb. 24, 1953 MANUFACTURE OF SULFURIC ACID Henry F. Merriam,West Orange, and Urban S. Lauber, Ridgewood, N. J., assignors to AlliedChemical & Dye Corporation, New York, N. Y., a corporation of New YorkApplication July 15, 1949, Serial No. 104,838

3 Claims.

This invention relates to improvements in manufacture of sulfuric acid.

The invention, its objects and advantages may be understood fromthefollowing description taken in connection with the accompanying drawingshowing diagrammatically apparatus in which a preferred embodiment ofthe process of the invention may be carried out. a

Referring to the drawing, numerals H, l2, l3, I4, [5, I6 and Hrespectively indicate a source of sulfurous material supply, an $02 gasgenerator, a cooler, a gas cooler and acid concentrator tower, a gascooling tower, a second gas cooling tower, and a drying tower. Gasgenerator or combustion chamber l2 may be any apparatus in whichsulfurous starting material is burned, decomposed, or otherwise treatedto form an S02 gas which is at relatively high temperature, e. g. 1600F, and usually much higher, contains substantial amounts of water vapor,and is suitable for use as S02 gas in the manufacture of sulfuric acidby the contact process. In a preferred embodiment of the invention, thesulfurous starting material is hydrogen sulfide gas. While such gas maycontain H28 in quantities as low as 25-30% by volume, preferably thesulfurous starting material is concentrated hydrogen sulfide gas havingan HzS content in excess of 85% by volume. Such gases are readilyobtainable in industrial operations and frequent- 1y have an H28concentration of 97-98% (dry basis). In the circumstance of use of HzSgas, generator 12 is any suitable form of a combustion chamber providedwith equipment enabling feed thereto of regulated amounts of H28 and airfor combustion supporting purposes. Cooler l3 may be of the radiatortype, or alternatively a waste heat boiler. Tower l4 may provide apacked chamber arranged for upflow of gas and downflow of cooling liquore. g. sulfuric acid. Gas leaving the top of tower l4 may be run throughline 20 into the topof an unobstructed tower or quench leg l5 in whichthe gas stream flows downwardly co-current with cooling liquid. The gasstream discharged from the bottom of tower l5 flows through line 2! intothe bottom of a second cooling tower l6 which may be arranged to affordupdraft gas flow countercurrent to cooling liquor. Tower II, into whichthe gas stream flows from line 22, may be a drying tower of any suitabledesign known in the art,i. e. constructed to provide for countercurrentflow of gas and sulfuric acid drying medium under conditions todischarge from tower l1 and into line 25 and S02 gas which may be driedto any desired extent in accordance the with the particular operatingconditions. Towers I4, l6 and H are each provided with liquor coolers26, 21 and 28 plus the necessary pumping and piping accessories (notshown) to effect controlled fiow and cooling of the liquors circulatedover the respective towers.

Numeral 30 indicatesa secondary combustion chamber into which the gasstream in line 25 is fed. The purpose and function of chamber 30 willhereinafter morefully appear. In one embodiment of the invention, amixture of sulfur vapor, S02 gas and nitrogen is formed in sulfur burneror sublimer 3|, and is charged into chamber 30 through line 33. The exitgas of chamber 30 is run directly through line 35 into converter 36, andthe gas stream is then passed through line 31, converter 38, line 40,and converter M in series, and into S03 conduit 42 as indicated on thedrawing. Undried air at atmospheric temperature is supplied to theprocess by a main blower 45 the pressure main 46 of which communicatesthrough valved connections 41, 48 and 49 with the HzS burner l2, andwith the interstage pipe connections 31 and 40 in the converter system.The S03 gas exiting converter 4| into conduit 42 is conducted thereby e.g. to an absorption system for making strong sulfuric acid, or to acondenser for condensing out any contained water vapor and an equivalentamount of S03 to thereby condense out H2804 and form dry S03 which maybe used in an oleum system or in a cong/entional absorber producing 99%sulfuric aci I A preferred embodiment of the invention may beexemplified as follows. An HzS gas containing about 96-98% HzS, some 002and possibly a trace or more of hydrocarbons is burned in primarycombustion chamber l2 with an amount of air preferably substantially inexcess of that theoretically required to oxidize the H28 to S02 and H20.Such air excess, which may be of the order of 50 to 90%, eflectscomplete combustion of the HzS and oxidation of any deleterioushydrocarbons which may be present, and also provides in the resultinggas stream further amounts of oxygen which are needed subsequently inthe process. The combustion chamber exit gas is at temperature generallynot less than 1600 F., and usually of the order of1800-2000 F. andhigher. A typical gas may have a temperature of 2000 F. or upwards, andcontain by volume (dry basis) about 8% S02, about 910'% oxygen, and asubstantial load of moisture. The amount of water vapor present in sucha gas is normally'substantially in excess of that needed to combine withall of the S03 (produced by subsequent catalytic oxidation of the S02present) to form 100% H2SO-1. Thus, the moisture content of the gasstream at this point may vary widely, and up to amounts which, if notremoved from the system, would result in formation of sulfuric acid ofstrengths as low as say 85% H2SO4. Consequently, to provide forproduction of strong e. g. 98-99% sulfuric acid or for S03 which may beutilized for manufacture of -oleum .a large portion or if desiredsubstantially all of the water present in the gas is removed.

The hot gas stream from combustion chamber I2 runs through line 52 tocooler I3 which may be designed to effect cooling of the gas down toabout 1000 F. The gas stream :is then fed into the bottom ofconcentrating tower I4 into the top of which is introduced sulfuric acidat temperature of the order of 250 F. and of H2804 strength of about say72%. During downfiow of the sulfuric acid liquor in the tower I l, wateris evaporated out of the acid which may run out of the bottom of towerI4 into line 55 at strength of about 72.5%. The gas stream leaves thetop of tower I4 into line 20 preferably at temperature of about 250 F.Whatever the particular design or construction .of the tower I I may be,countercurrent flow of acidand gas therethrough should be controlledpreferably so that the acid strength increases preferably about 0.5% inH2504 value, and the gas is cooled down to within the range of 240-260F.

The gas is then charged into the top of an open quench tower or leg I5into the top or which is fed from line :58 a spray .of water which maybe initially at temperature of about 100 F. The gas and waterflowco-current through tower is, cooling the gas andcondensing some ofthe water content thereof. The water as discharged from the bottom oftower I5 through line 60 may be at temperature of about 130-140 F. andconta1n l-2% H2804. Such water may be cooled and recirculated over towerI5 orbe discarded.

The gas stream leaving the bottom of tower 'I-'5 is introduced into thebottom of the second cooling tower IE into the top of which is fed watercontainingsay l-2% .H2SOA at temperature initially of about .100 F. fromline 58. During countercurrent flow of water and gas in this tower, the:gas stream ,is cooled down to about I 100 and most .of the waterthereof is condensed out, the liquid effluent at the bottom of the towerin line 52 being at temperature of about 130-140" .F. and containing e.g. 1-2% H2804. The greater part of such water may be cooled andrecirculated over towers I5 and I6, and the make of tower I6 isdischarged through line'65 to waste. Overall control of the .eooling intowers I5 and I6 is preferably such that the gas stream leaving tower I6through .line 22 :is at temperatures as close as practicable toatmospheric temperature. While about 100 F. anaverage sought-for value,this temperature may vary from say 80 to 120 F. In any .case, :the watercontent of .thegas at this point is reduced to saturation at thetemperature of the .1328 leaving the tower, e. ,g. the water content.may vary from 0.8 to 2.00 grams H2O per cu. ft. .of gas. Thus, the gasentering tower I6 may contain the water vapor presentin the air used forcombustion in'generator I2, the water vapor formed bycombustion of.-H2S, and water evaporated out of the acid in the concentrating tower@114. ,Accordingly, itwill be seen that towers I5 v and I6 effect theremoval from the gas stream of the great bulk of the contained water,all of which water is discharged from the system at a single point,namely outlet 65.

The next step in the process is the drying of the gas stream to anextent which permits use in all subsequent stages of the process ofundried atmospheric air but nevertheless makes about 65-70% of the S03,ultimately formed, available for fortification of weak acid ormanufacture of oleum, the balance of the SO: being available formanufacture of 66 B. or 99% sulfuric acid. Drying the gas stream to theextent desired may be effected by feeding into the top of tower I!through line I0 sulfuric acid of strength preferably in the range ofabout 67-70% H2804, and at temperature .in the neighborhood of F. orless. During countercurrent flow of gas and drying acid in tower I I,the gas is dried substantially but not necessarily thoroughly, and thegas stream leaves the top of the drying tower at temperature of about120 F. Drying acid is discharged from the bottom of the tower at astrength which maybe in the range of 66.5-69.5% H2804, and have atemperature in the neighborhood of 13.0 F. Normally the gas dischargedfrom tower I! may contain water vapor in the amount of about 0.3 gramper cu. ft. of gas. In a preferred embodiment, countercurrent flow ofgas and drying acid in tower I1 is regulated so that the gas dischargedtherefrom is at temperature in the range of about 115 F. to about F. Inthese circumstances, when feeding into the top of tower drying acid ofstrength in the range of 67-70% H2304, drying acid H2804 strength in.one pass through the tower is reduced about 0.5%.

Some of the weakened drying acid is drawn ,out through line 12 and isfed through connection I4 into the circulating system of concentratingtower I4. While in the liquor circulating system of tower I4, theweakened drying acid is concentrated back up to strength of about71-73%. Part of the acid recirculated in the system of tower I 4 isdrawn out through connec- 'tion '16 and'run back into the liquorcirculating system of the drying tower to maintain the strength of thedrying acid. By recirculating acid fromthe drying tower back to theconcentrating tower and then forward to the drying tower, water pickedup in the acid in the drying tower is transferred backinto theconcentrating tower, evaporated outof the acid and carried by the maingas stream into towers I5 and I6 in which such water is condensed out ofand ultimately discharged from the process.

The; gas stream leaving drying tower I! through line 25 contains, inaddition to some .moisture, substantial quantities of sulfuric acid mistderived from moisture and small amounts of S03 incidentally formed inthe combustion chamber. In accordance with the invention this mist ischanged to a non-deleterious form by treatment of the gas stream in thesecondary combustion chamber 30. The latter may be of anysuitableconstruction or design provided that the portions thereof in directcontact with the gases are built of refractory material such asfirebrick of various types. The exterior of chamber 30 may be insulatedto minimize heat losses.

-In chamber 30, the gas stream containing the sulfuric acid mist,isabruptly heated to temperature appreciably above the dew vpoint ofthe acid mist under the particular conditions of operation. Ordinarily,temperature rise in the secondary combustion chamber is effected to suchan extent that temperaturespnevailing in chamber 30 are atleast 700 F.Preferably-higher temperatures are utilized, and heatingof the gasstreamis such as to raise the temperature thereof to at leastapproximating but not Substantially in excess of, initialconversion-temperature Specifi-- cally, the preferred temperatures inchamber 30. areof the order of 750-850? F. By so proceeding,

the. invention. aifords several advantages. The.

toremove the excessive amounts of water vapor formed by combustion of--H2S. L This cooling results information of Hz'SOr mist which would.destroy heat exchangers normally used for heating the burner gas toinitialconversion tempera ture. Such heat exchangers areelirninated bythe useof heatingchamber 30.v Further, the temperature of the gas streamat the same. time is raised to initial conversion temperature whichpermits introduction of "the exit gas-offlthe combustion chamberdirectly into the converter sys-. tem. More importantly, the improvedprocedure provides for elimination of the relatively expene sivelyconstructed'coke box or precipitator heretofore employed for separationof acid 'mist. In prior methods utilizinga-cokeflbox for separation ofacid mist, it was apractical necessity, in" order to avoid prohibitivecoke, box construction costs, to design the plant as a' whole so -as ftoprovide for operation of the coke box'lat a slight or 'ap-j preciahleminus pressure. Plants of this nature involve the use of a drying'towerfollowing the. coke box," and then a blowerthe suction side or:

which is connected with thejex'itj of the drying tower and the pressureside of which communicates with the inlet of convertersystem' Inthejseprior methods, regardless of goodcokebox'and drying tower operationpractice, at times traces of acid mist may pass into and through. the

blower with damaging results; Inthe presentimprovements, the coke box isreplaced by a-secon'darycombustion'chamber which may be relativelycheaply constructed and yet operatedum der'positive pressure. Thus, theinvention provides for elimination of heat transferrers and the cokeboxesf used in conventional sulfuric acid systems where cooling andpurification of gases are required to eliminate water vapor. Further,elimination of the coke boxmakesdt possible to operate the entire plantunder positive pres sure and place the blower, suchas 45 of the drawing,at the head of the system, a point where the blower is required tohandle only at atmospheric air, and is not subjected to the corrosiveeffects of any acid mist whatsoever.

Adequate temperature increase of the .gas stream in chamber 30 maybeeffected in several convenient ways. For example, a brimstone sublimeror burner indicatedat '31 may beemployed. Such burner may be ofconventional construction, andoperated in such a way'as to produce inexit .line 33 a mixture of sulfur vapor, S02 gas and nit-rogen. Inoperation, brimstoneand permissibly undried atmospheric airare fed intothe inlet end of the burner in the usual manner. Ihe gas-mixtureproduced and discharged into line 33may=contain for-example about 18%sulfur dioxide, about 14% sulfur vapor by volume calculated as S8, theremainder being nitrogen. This mixture of hot sulfur dioxide and sulfurvapor is charged into a chamber 30 and, at the temperature prevailingtherein, the sulfur vapor is burned to $02 liberating heat in suflicientquantities to maintain in chamber 30 the tem-:.

peratures desired for the particular situation at hand. It will berecalled that in the operation of primary HzS burner 12, a substantialexcess of air is utilized. The oxygen of such air passes through thesystem previously described, enters chamber 30 through line 25, and isadvantageously utilized in chamber 30 to support combustion of thesulfur vapor introduced through line 33. In a typical run in which anexcess of e. g. say- -70-80% of air is employed in the primarycombustion chamber l2, introduction of extrane ous air into secondarycombustion chamber 30 is unnecessary, since the inflowing gas streamfrom line 25 already contains sufficient oxygen to support combustion ofthe elemental sulfur fed into chamber 30. If, for some desired reason, asubstantial excess of air is not employed in primary combustion chamberl2 additional needed quantities of air may be charged into a chamber 30through valve controlled line 8|]. In view of the permissibly widelyvarying conditions which may exist in chamber 30 with respect tocomposition of the gas stream in line 25 and the size of the operationat hand, it is not possible to delineate limits as to composition andquantityof the sulfurous material introduced into chamber 30 forcombustion and resultant temperature raising purposes. The control pointof operation is the temperature of the composite gas exit-. ing chamber30 into line 35, and regulation of burner 3| may be gauged accordingly.Such temperature should lie within the range of about 700-850 F., and ispreferably about 800 R, an

average initial conversion temperature. In the specific procedure of theinvention being exemplified, the gas exiting chamber 30 may containabout 11% S02, about 7% oxygen, i. e. sufficient oxygen for theoreticalcatalysis of S02 but insufe ficient for commercial catalysis of the S02.While, as stated above, it is preferred to operate the combustionchamber [2 with a substantial excess of air, preferably this excess islimited so that the exit gas of chamber 30 is deficient in oxygen forcommercial catalysis of S02. This feature reduces the volume of gashandled in chamber 30, the amount of sulfur vapor burned therein fortemperature raising purposes, and also the size of chamber 30. l

, In certain circumstances of commercial operation, introduction ofappreciable amounts of water into the gas stream is not objectionable,and in such situation temperature increase in chamber 30 may be effectedby introduction and combustion of suitable amounts of H25 gas, e. g.,thev same HzS gas as fed into chamber I2. Here again, the amounts of H23gas fed into chamber 30 may vary widely but, as in the case of -utilization of sulfur burner 3|, quantities of HzS fed into chamber 30should be such as to create and maintain therein the temperatureconditions already stated. In a further modification, temperatureincrease in chamber 30 may be effected by adjustment of the valves inlines 52 and 82 so as to bypass from the exit line of combustion chamberI2, through line 82, certain quantities of the exit gas of combustionchamber l2. As previously noted, such gases are ordinarily at the hightemperatures of 2000 F. or more,'and in accordancewith this modificationthe sensible heat of an increment of primary combustion chamber exit gasis utilized in chamber 30 to raise the temperature of the composite gastherem to the temperatures previously noted. In the fled in whichthe gas:leaving the chamber I 2;

contains about S02 -and'about 8% oxygerr and is at temperature of about20009' F.', and-the gas entering the secondary'chamber; 30 isat.temperature of approximately 100-120 F.,. the quantity of gas by-passedfrom chamber" I through line 82 into chamber may betabout one volume pertwo volumes of gas fedinto' chamber SO/through 1ine"-25.

Returning to the principal modification being described; 1. e. use ofsulfur burner: 3 I, about conversion" of S02 to S03 may be. effected :in:con-s verterJ'36 and temperatureiof therexit: gas thereof. maybe about1100 F. Undried air. isintroduced; into connecting" line 3-7 in quantitysuflicient:;to. bringthe temperature of the gas stream enteringconverter 38to about 800 F., in whichinstance: thegas'entering converter30 may contain about 8% SO and 11% oxygen. In converter. 38; around 90%overall conversion is. affected and the gas exit thereof may be attemperatureofaround 950 F. Additional undried air is-introduced throughline 49 in quantity sufiicientlto. reducethe temperature ofthe gasentering converter-dl to about 800 F., in which casethegas stream maycontain around 6-7 S02 and about.

133% oxygen. Interstage introduction of air-elim inates'use of heatexchangers. Moreimportantly this feature provides'for introduction into'the converter system of a relatively large proportion of the totaloxygen needed for commercial ca;- talysiswithout-the necessity ofpassing all of'the air to satisfy oxygen requirements. through chamber35, thus facilitating further the-size reduction of secondary combustionchamber '30 as referred to above. In converter 4|, approximately- 98% orbetter overall conversion to S0; iseiiected, and the gas stream exitsconverter '41 at temperature in the range of 800-850" F. As previouslynoted, such a gas may be utilizedin conventional absorbing towers toproduce strong sulfuric acid, or may be employed in so-called condenserswhich condense out, as strong sulfuric-acid, the water vapor contentofthe gasstream with an equivalent amount-of S03 and producea condenserexit containing substantially dry-S03 gas-which may be used in anoleum-producing system.

We claim:

1. The process for making sulfur trioxide which comprises burningsulfurous material to form an initial hot gas stream havingtemperature-not less than 1600 F; and containing SO:

and acid mist forming constituents anda-sub'-' stantial quantity of H20,cooling said gas-stream to'not higher than about 120 F. to condense outmost of said H20 and form acid misncontacting saidgas stream containingsaid'mist with sulfuric acid drying medium to further dry said gasstream and form an S0; gas attemperaturesub stantially. below initialconversion temperature and containing said sulfuric acid mist, burningin said'SOz-gas containing said mist; while. in-a refractory chamber;sulfurous material inxquani-e tity. sufiicientrto raise the temperature.of the re+ suiting composite S02 gas totemperature atleastapproximating but not substantially in excess or initial. conversiontemperature to thereby vaporize said acid mist to: change the-same.- tononedeleterious form, and then catalyticallycom vetting- ::vafraid-compositegasrsto: the entire foregoing: operation" being carriedout at positive pressures andi by utilization of undi'i'edatmosphericair asthe oxidizing medium; a

2. The process for. making sulfur-- trioxide' which comprises burningsulfurous' material to form" an initial hotitgiasstreamahaving temperatture--not-1ess'-'than 1600 F; and containing S05 and acidmisttformingconstituents-and asubstantial quantity:of H20; cooling; said gasstream toz notrhigher than about i F. to' condense'fiout most'of saidiHzO and form acid mist, contacting said gasstream containing saidimistwith: sulfuric acid drying medium to further drysaid gas stream and forman" SOrgasat temperature sub-- stantiallybelow" initial conversiontemperature andcontaining said sulfuric acid" mist, burning in said S02gas containing. saidmist; ,while ima' refractory-chamber;ielementalsulfur inquaiitity sufiicient to raisethe"temperature-of themesult' Ieterious'form; and'-then catalyticallyconvertingSOz-ofsaid'composite.gastOtSOir, the entirefore going operationbeingcarried'outat positive pres sure" and by utilization of undri'ed"atmospheric airf'as'the." oxidizing'jmedium;

' 3; The: process for: making. sulfur" trioxide' whichcomprises"burning'concentrated H'zS gas to form an .initialjhot' gasstream. havlngtempenature noti'lessthan 1.1600 l5. and'containingr SO:and acidmist forming constituents and" a. substantia-lquantity ofiHzD,coolingsaid gas stream to not: higher than aboutr120FJ to condense outmost of said Hi0? andiorm acidmist; contacting said'gas streamcontaining saidipmist with sulfuric aciddiying-mediumto furtherdrysaidfgas stream and' form an sOzgas. at temperature substantiallybelow initial conversion temperature and containing said sulfuric acidmist; burning in said :SOi. gas. containing said"mist.. whil inarefractory chamben. gaseous. His? in. quantity suflicientito raise thetemperature of the resulting composite. S02 gas. vto temperature. atleast approximating, but not substantially. in. excess of. initial?conversion temperature to thereby. vaporize said acidfjmist. toch'angethesame to non-deleterious form,.andthenlvcatalyticallyconvetting; S02 .01 said" composite gas. to. $04... the entireforegoing. operation being carried out at positive pressure and byutilization.of undried atmospheric air. as the oxidizing medium.

HENRYT: MEIRRIAM?v URBANJSL LAU'BER';

REFERENCES? CITED The; following referencese-arew ofrecord in the me. ofthis. patent UNITED L STATESJPA'I'ENTS I,

Number Name Date 1,737,320 Merriam Nov;26, 1929 21044;419 Clark" J une-'16 1936 2,079fl60 Carl May 11; 193-! FQREIGN 1' PATENTS Number:Country;- Date 367,381; Great'Britain; Feb: 19,1932

